[Backup/Dashboard] add new snackbar

[AdrianBLK]

On the Dashboard screen the user sees the snackbar about the new option to backup wallets:

• display rule: notification always present on this screen
• position: bottom of the screen
• text: Backup now your secret phrase on your Google Drive account
• button: BACKUP
  (displayed right of the text)
• click on the button triggers the Backup Walelt flow

Sketch screen here